The light emitted in the transition $n=3$ to $n=2$, (where $n$ is the principal quantum number of the state) in hydrogen is called $\mathrm{H}_\alpha$-light. Find the maximum work function that a metal can have, so that $\mathrm{H}_\alpha$-light can emit photoelectrons from it.

A light of wavelength 310 nm is used in a photoelectric experiment. The metal electrode of work function of 2.5 eV is used in the experiment. The stopping potential for the photoelectrons will be (assume, $h c=1240 \mathrm{eV}-\mathrm{nm}$ )

A radiation of energy $E$ falls on a perfectly reflecting surface. The momentum transferred to the surface is (let $c \equiv$ speed of light)